1. Field of the Invention
The present invention relates to a method for cutting curved surfaces which is applicable when a cutting process is employed to form curved surfaces of lenses and metal mold surfaces for forming lens surfaces of lens forming metal molds. Also, the present invention relates to lenses and lens forming metal molds formed by cutting processing.
2. Related Background Art
Lens surfaces of objective lens that may be used for optical pickup apparatuses or the like, or metal molds for forming such lens surfaces are typically formed by copying machining by a copying lathe. A bite that is used in the lathe machining has an arcuate cutting edge, and the cutting edge of the bite is moved along a curve that copies a desired lens configuration. Also, when a lens surface is to be provided with a blazed configuration, the lens surface and stepped configuration of the blaze are cut by a bite having an arcuate cutting edge with a cutting edge angle being pointed as sharp as possible.
When lens surfaces of a lens are cut by using a bite that is equipped with an arcuate cutting edge, a cutting edge region of the cutting edge that abuts against the surface of the lens material is moved along the lens configuration during the cutting processing. For this reason, when such cutting work is performed by a lathe, corrections of configuration are necessary based on the cutting edge radii of the bite and the lens configuration.
Also, since the cutting region of the arcuate cutting edge moves according to the lens configuration, it is difficult of create correction data by directly feeding back measurement results by a configuration measurement apparatus that is generally used.
Furthermore, since the arcuate cutting edge is pressed against the surface of the lens material in a point-contact state to cut the surface, cutting regions of the arcuate cutting edge that are used for cutting would likely become one-sided depending on the lens configuration, in other words, the use frequency of cutting portions in the arcuate cutting edge may become non-uniform. When the use frequency of cutting portions in the arcuate cutting edge is not uniform, portions that are more frequently used worn out more quickly, and the wears become non-uniform, and the service life of the bite shortens.
Furthermore, blazed sections are cut in the lens surface by a bite having an arcuate cutting edge with a corner section that is formed by partially reducing the radius of curvature of the arc of the arcuate cutting edge as small as possible. However, when the lens surface is cut, a cutting edge section adjacent to the corner section in the arcuate cutting edge is mainly used. For this reason, the corner section and portions of the arcuate cutting edge adjacent to the corner section are worn more quickly. When wears at the corner section and portions of the arcuate cutting edge adjacent to the corner section increase, die wears are formed at corners of the formed blazed steps, and the steps cannot be accurately cut.